Magnetically coupled pushbutton switches are commonly used with short travel keypads and keyboards. They provide good tactile feedback to a user, are compact, discrete, and have a long life. These switches, exemplified in FIGS. 1-4, normally have an electrically conductive armature 2 that is magnetically held by a coupler magnet layer 4 in a rest position, as in FIG. 1, spaced from switch contacts 6 on a non-conductive substrate layer 8. A user-provided actuation force applied to a crown 10 of the electrically conductive armature (usually stamped sheet metal that is silver plated) causes it to snap free of the coupler magnet layer and close the switch contacts by electrically connecting them. Release of the actuation force allows the coupler magnet layer to attract the electrically conductive armature back to the rest position to reopen the switch A nonconductive spacer layer 12 (such as high density foam) is fixed to the substrate layer, with a cavity 14 in the spacer layer exposing the switch contacts. The coupler magnet layer overlies the spacer layer. The electrically conductive armature is magnetically coupled to the bottom of the coupler magnet layer so that the electrically conductive armature is housed within the cavity in the spacer layer. The armature""s crown protrudes through an aperture 16 in the coupler magnet layer. Typically, a polyester membrane layer 18 with suitable graphics overlies the coupler magnet layer to seal the switch and to direct a user of the switch as to location and function of the switch
Magnetically coupled pushbutton switches of the prior art, as shown and described in U.S. Pat. Nos. 5,523,730, 5,990,772, 6,262,646, 6,466,118 and 6,556,112, all have an electrically conductive armature that can travel through a unique pivot/click (FIG. 2/FIG. 3) movement designed to create a very distinct tactile feedback to a switch user. This distinct tactile feedback, inherent to the design, is necessary for the proper function of the switch because the electrically conductive armature 2 is responsible for electrically connecting the exposed switch contacts 6 on the substrate layer 8 of the switch FIG. 2 shows that application of an actuation force 20 causes a heel 22 of the electrically conductive armature to break away from the coupler magnet layer 4 and travel to the substrate layer 8 where the heel stops and functions as a fulcrum for the electrically conductive armature. FIG. 3 shows that continued application of the actuation force causes a toe 26 of the electrically conductive armature to abruptly break away from the coupler magnet layer so that the toe contacts the substrate layer and the electrically conductive armature electrically shorts the switch contacts formed on the substrate, thereby actuating the switch
The present invention is a magnetically coupled pushbutton plunger switch that is discrete and may be used with a keyboard, or anyplace there is limited space. There are several unique characteristics of the present invention that are, for some applications, more preferable than the prior art. A first benefit of the present invention is the ability to seal the electrical conductors of the switch without the use of a polyester membrane overlay that can add undesired pre-load and prevents the use of hard keycaps. A second benefit of the present invention is that the armature does not need to be electrically conductive, or silver-plated, because the armature is not a part of an electrical circuit, unlike the prior art A third benefit of the present invention is that the pivot/click motion has been eliminated, so there is no double tactile feedback to a switch user.
In the preferred embodiment of the present invention, a post attached perpendicularly to a keycap is moveably mounted inside a sleeve attached perpendicularly to a base such that the hard keycap and base lie in substantially parallel planes. A magnetic coupler, fixed to the bottom surface of the base, magnetically attracts a magnetic armature that is secured to the bottom end of the post. When a user-provided actuation force is applied to the top of the hard keycap, the magnetic armature evenly breaks away from the magnetic coupler in one motion, similar to the way that a suction cup abruptly breaks away from a smooth surface when pulled perpendicular to the surface. After the magnetic armature breaks away from the magnetic coupler, it travels into physical contact with a sealed membrane switch assembly. Contact with the membrane switch assembly causes opposing electrical conductors to electrically connect, thereby closing the switch. As used herein, the term xe2x80x9ctopxe2x80x9d refers to that surface of any part in a cross sectional figure of the drawings that faces the top edge of the page, while xe2x80x9cbottomxe2x80x9d refers to that surface of any part in a cross sectional figure of the drawings that faces the bottom edge of the page.